Tate Donovan, a geek biochemist with no luck at all with women, is persuaded by his friends to visit a gypsy, Madame Ruth. She gives him "Love Potion No. 8", an elixir which can potentially force anyone of the opposite *** to instantly fall in love with him. He shares the potion with his friend, Diane, and together they embark on a "scientific evaluation" that gets out of hand.